The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Today many companies, e.g., utility companies such as telecommunication companies, electrical utility companies, gas companies, water companies, sewer companies, etc., bury their respective products, or structures, underground. Locating such structures is useful when repairs to the structures are needed and to avoid hitting the structures during subsequent excavation. However, often such structures are made from non-metallic components such as fiber optic cable which can make subsequent identification of the location of such buried structures difficult. Therefore, to make the location of these underground structures easier, companies and utilities often use underground passive electromagnetic markers that can be buried with the structures, i.e., buried next to, adjacent or near the structures, as the structures are being installed and buried. These markers can subsequently be located, and hence the location of the structures can subsequently be identified, with a specialized locating device from above the ground.
There are several known variations of such underground markers. Typically, such markers operate on various standard frequencies such that markers of a certain frequency will be buried with specific structures so that the location of specific structures can be easily and readily identified. Often, the outer shells of the markers can be color coded to correlate with the different frequencies and corresponding structures.
This disclosure provides a new method of leveling the coil inside an underground marker. Previous markers have floated coils on water to ensure the coil is level with the surface. This method requires multiple sealing tasks and creates a marker which is very heavy. Others use three separate coils for each axis to create a spherical field which doesn't need to be leveled but requires three times the components. This new method uses a gimbal solution which mechanically levels the coil with the use of only two inner plastic pieces and one sealing operation.
Generally, the markers comprise a coil connected to an inductor/capacitor (LC) circuit that will resonate and generate an electromagnetic field when subjected to an electromagnetic pulse generated by the locating device. The electromagnetic field generated by the marker can then be detected by the locating device to identify the location of the respective structure. Typically, the electromagnetic field generated by the marker will have a dipole shape and it is important that the orientation of the coil within the marker be such that the dipole shaped electromagnetic field will be generated upward toward, and substantially orthogonal to, the ground surface, as opposed to sideways and substantially parallel to the ground surface. Therefore, to avoid having to carefully orient each marker in the ground as it is being buried, some known markers are typically self-orienting. That is, the markers are constructed such that marker can be tossed into the trench next to the structure and the coil will self-orient within the marker such that the dipole shaped electromagnetic field generated by coil (i.e., the LC circuit) will extend upward, substantially orthogonal to the ground surface.
One known design of such a self-orienting marker floats the coil on a liquid within the marker, whereby the coil will self-orient within the marker such that the electromagnetic field will be generated upward toward the ground surface. Such a method is described in U.S. Pat. Nos. 4,712,094 and 6,246,328. Another known design uses three independent coils that are oriented in a three-axis arrangement (i.e., oriented in an X-Y-Z axis arrangement). This creates a spherical field around the marker such that the orientation of the marker is not important. Such a method is described in U.S. Pat. Nos. 5,699,048 and 6,097,293.
The underground marking industry has become very cost competitive and many customers select the markers based solely on the cost. With hundreds of thousands of markers being sold every year, any reduction in assembly time or material cost can become a large competitive advantage.
Moreover, the several known buried markers in the industry and generally each use free wound coil designs that must be carefully inserted inside a coil holder of the marker. These free wound coils must also be secured inside this holder to ensure the coil doesn't distort its shape when the marker is dropped in to the trench of the buried structure. Another known marker type utilizes coils wound around a ferrite rod, which provides a strong mechanical surface for the coil, but ferrites are expensive and difficult to wind around. Ferrite coils also do not provide an ideal radiated field for underground locating.